Natural and synthetic polymers such as collagen, soya, glycerol, silicone, polyvinylpyrolidone and hyaluronic acid have been utilised as endoprostheses. Materials used for endoprostheses generally try to imitate the natural soft tissue and are intended to be safe to the health of the patient.
Polyacrylamide gels have also been disclosed. U.S. Pat. No. 5,798,096 relates to a biocompatible hydrogel containing 3.5 to 6.0% cross-linked polyacrylamide. However, U.S. Pat. No. 5,798,096 teaches that concentrations below 3.5% make the hydrogel unstable.
GB 2114578 relates to a polyacrylamide gel for medical and biological purposes containing 3 to 28% polyacrylamide with the remainder of the mass of the gel comprised of a physiological solution.
U.S. Pat. No. 5,658,329 relates to an implantable endoprosthesis comprising a shell filled with a polyacrylamide gel comprising 2 to 20% polyacrylamide by weight and a viscosity range of 15 to 75 Pas.
Formacryl® polyacrylamide is a soft-tissue endoprosthesis consisting of 5% reticulated polyacrylamide polymer and 95% apyrogenic water commercialised as an injectable device for medical and dental use to correct congenital or acquired deficits such as wrinkles, lines and scars. It is to be implanted with a syringue in the hypodermis.